Vadnais Engineering

Although the effect is usually unintentional, a single image may be deceptive!

In the photograph below, both the height and the angle of the camera seem to indicate that the subject SUV was a two-door model. But actually, there was no such vehicle as a two-door 2004 Chevrolet Trailblazer. In fact, the subject shown here was even the extended EXT version of the standard four-door. (Note the top of the chopped off B-pillar visible above the window frame, which is the clear giveaway that it is actually a four-door SUV.) [Click on image to enlarge, then click back arrow to return to post.]

It is standard practice to make multiple photographs around every subject vehicle. It’s also often necessary to make images at different heights and angles. No one who sees all of our photographs will be deceived. The problem is when you get only one or maybe a couple photos of a subject you either haven’t or can’t inspect yourself.

Using the same prime ZEISS 50 mm lens at the same tripod height, the photo below clearly shows the vehicle was a four-door. [Click on image to enlarge, then click back arrow to return to post.] 

This unintended deception isn’t an issue when you’re making your own photographs, but it can be a problem if you’re trying draw conclusions based on a limited number of photographs provided to you. This frequently happens when the vehicle has been destroyed or is otherwise unavailable, and only one or a couple photographs—often made with a cell phone—are all the evidence that remains.

Takeaways:

-1- Be careful making conclusions based on a single photograph.

-2- Make a series of images around the entire circumference of any vehicle or subject you are documenting.

SAE International is hosting a FREE Accident Reconstruction Digital Summit on March 29 and 30, 2022. There will be presentations on a wide variety of current issues and areas of interest to anyone working in or with accident reconstructionists, including law enforcement, engineers, attorneys, and insurance adjusters.

From 1:45 to 2:15 pm EDT on Wednesday, March 30, I’ll be presenting on the importance of using a tripod, a polarizer, and a flash during inspections in the field, in storage facilities, and in the lab. The use of those tools can result in superior images—in the camera—with detail and data you can’t extract or replicate later in post-production. Best of all, you can put those three tools to work immediately, which will make your photographs consistently better and more useful.

Here’s a link to the Summit: SAE Accident Reconstruction Digital Summit. Again, registration is free and available here: SAE Accident Reconstruction Digital Summit Registration. I hope to virtually see you there!

By the way, my presentation will be just a snippet of what we’ll cover in my three-day SAE Forensic Photography class. Now that SAE will be resuming in-person classes this summer, I’ll post the next class dates as soon as they are finalized.

While this is hardly news, on sunny or lightly overcast days, the positions and sizes of the shadows of trees, buildings, signs, poles, fences, guardrails, etc., change throughout the day. At certain times, these shadows can make it difficult to clearly show tire marks, paint marks, or gouges in your photographs. The worst is when there is a pattern of light and shadow across your scene.

This first image was made at 10:21 am on a mostly sunny morning. (Click on image to enlarge. Then click back arrow to return to this post.)

This view was made looking south, so the morning sun would have been to left, or east. The dense line of trees on the eastern edge of the road cast a shadow across the entire road with bright spots through the openings in the branches. These bright spots can interfere with details or evidence you might want to show.

Returning to that same scene at 2:45 pm that afternoon, the overcast had burned off. Even though the sun was quite bright, it was at an angle that evenly illuminated a lot more of the road, with only some shadows at the left. (Click on image to enlarge. Then click back arrow to return to this post.)

By late afternoon that day, it had become too overcast for deep shadows, so I went back a couple afternoons later to capture what that scene would look like later on a sunny day.  The image below was made at 6:52 pm. (Click on image to enlarge. Then click back arrow to return to this post.)

Those seemingly innocuous trees to the west (right of the photo) were now casting long, separated shadows across the road. These shadows would obviously make it more difficult to show gouges, tire marks, or even paint marks on the pavement.

Time permitting (i.e., it’s not a rapid response), it’s worth checking out where the sun and any shadows would be before you set out to inspect a scene.

For many years, I’ve been using The Photographer’s Ephemeris (TPE) https://photoephemeris.com/en to determine where the sun is going to be in relation to any accident site. (It’s now a subscription service, and well worth the small cost.) It’s extremely valuable if you need to show whether the sun could have been in the eyes of any drivers or witnesses.

And as in this case, it’s also useful for determining when you have the best chance of getting clean site images with minimal shadows. Below are the three TPE screen captures that show what information you get.

The first shows where the sun was when the 10:21 am photo (top one above) was made. (Click on image to enlarge. Then click back arrow to return to this post.)

The line of the sun is shown as the narrow gold line coming in from the lower right toward the pin marking where my tripod had been set up. Note that while the photographs were made looking south, the TPE diagrams have north at the top. So the morning sun in the east will be from the left side in the photos and from the right side in the TPE diagrams. (Just FYI, the wider yellow line at the upper right was the sunrise angle while the wider orange line at the left was the sunset angle.)

This diagram showed that at 10:21 am on 09/04/21, the sun would have been coming in from the eastern side of the road through a thick area of trees, which is exactly what was shown in the top photograph.

At 2:45 pm on the same day, the sun was beyond the thick trees to the east, yet below the tree line to the west. This should result in a photograph with minimal shadows on the road, as the second photo above shows. (Click on image to enlarge. Then click back arrow to return to this post.)

When I went back a couple days later at 6:52 pm, the TPE diagram showed that the sun would now be far enough west that it would come through the line of single trees to the west once the sun got low enough in the sky. Once again, that is precisely what the third photo above illustrates. (Click on image to enlarge. Then click back arrow to return to this post.)

TPE gives both the azimuth and altitude of the sun. In this post, I’m only using the azimuth for direction, and applying a general knowledge of how high the sun will be from experience. For a question about whether the sun was in a driver’s eye, you’ll have to use both azimuth and altitude. That’s a future post.

TPE has many more sophisticated applications, including using AI to show where the sun or moon will be in a scene. It’s well worth getting and exploring all of its features. (I have no ties to TPE nor receive any compensation from them. It’s just a great tool I highly recommend.)

Takeaways:

-1- Before you photograph your wreck site, it’s often worth determining when the sun will cause the fewest or shortest shadows on your road.

-2- The Photographer’s Ephemeris is well worth using when you need to know where the sun will be at specific times on specific dates.

Photographs of collision sites in most intersections, or in residential or commercial areas, will have recognizable elements that orient a viewer to that area. Conversely, many stretches of rural roads, interstates, or other limited-access highways have few, if any, distinctive features. While it will be assumed that your photos show the road where the wreck occurred, without visible landmarks, it may be difficult for viewers to relate to the area. Signs, bridges, guardrails, and other roadside objects can be helpful—but only if you include them in your photographs.

As an example, the top of a fireworks store is partially visible at the top of the image below, but it isn’t visible enough for a viewer to determine where this photograph was made. [Click on photograph to enlarge, then click on Back arrow to return to this post.]

By the way, this photograph was made for two purposes. First, it showed the roadway in the direction the accident vehicles were coming from. Second, it showed an oncoming vehicle as it crested the hill (vertical curve) on the approach to the area of impact to give a sense of the sight distances involved.

While the fireworks store is a partial clue, the timing of the tractor trailer in the above photo obsured an exit sign, visible below, that would definitively place where the photo was made to someone generally familiar with the area. [Click on photograph to enlarge, then click on Back arrow to return to this post.]

Unless you intend to depict the effect of obscuring an element at a site, which sometimes you may wish to do, it is worth making a habit of reviewing your images while you’re still in the field to ensure you haven’t accidentally masked an important feature you meant to show.

Five takeaways:

-1- You should make photographs of the approach to a wreck scene to establish where the vehicle or vehicles came from.

-2- If a hill, curve, tree line, building, etc., obscures the view of an approaching vehicle, in any direction, you may want to capture the view both without any vehicles and then with a vehicle just coming into view to assist in visualizing the visibility distance.

-3- Especially on a rural road or on a limited-access highway, photographs including signs or other roadside features can help a viewer relate to where the photo was made.

-4- You can time your photographs so that passing vehicles will or will not obstruct certain roadside features at an accident site, depending on what you are trying to illustrate in each photo.

-5- You should include unobstructed permanent roadside objects in at least one photograph so you won’t be embarrassed by failing to fully document a wreck site.